Index: lld/trunk/COFF/Config.h
===================================================================
--- lld/trunk/COFF/Config.h
+++ lld/trunk/COFF/Config.h
@@ -179,6 +179,7 @@
   bool AppContainer = false;
   bool MinGW = false;
   bool WarnLocallyDefinedImported = true;
+  bool Incremental = true;
 };
 
 extern Configuration *Config;
Index: lld/trunk/COFF/Driver.cpp
===================================================================
--- lld/trunk/COFF/Driver.cpp
+++ lld/trunk/COFF/Driver.cpp
@@ -547,6 +547,12 @@
   std::string LibName = getImportName(AsLib);
   std::string Path = getImplibPath();
 
+  if (!Config->Incremental) {
+    HandleError(writeImportLibrary(LibName, Path, Exports, Config->Machine,
+                                   false, Config->MinGW));
+    return;
+  }
+
   // If the import library already exists, replace it only if the contents
   // have changed.
   ErrorOr<std::unique_ptr<MemoryBuffer>> OldBuf = MemoryBuffer::getFile(Path);
@@ -907,6 +913,7 @@
   // Handle /debug
   if (Args.hasArg(OPT_debug, OPT_debug_dwarf, OPT_debug_ghash)) {
     Config->Debug = true;
+    Config->Incremental = true;
     if (auto *Arg = Args.getLastArg(OPT_debugtype))
       Config->DebugTypes = parseDebugType(Arg->getValue());
     else
@@ -1113,6 +1120,9 @@
   Config->AllowBind = Args.hasFlag(OPT_allowbind, OPT_allowbind_no, true);
   Config->AllowIsolation =
       Args.hasFlag(OPT_allowisolation, OPT_allowisolation_no, true);
+  Config->Incremental =
+      Args.hasFlag(OPT_incremental, OPT_incremental_no,
+                   !Config->DoGC && !Config->DoICF && !Args.hasArg(OPT_order));
   Config->NxCompat = Args.hasFlag(OPT_nxcompat, OPT_nxcompat_no, true);
   Config->TerminalServerAware = Args.hasFlag(OPT_tsaware, OPT_tsaware_no, true);
   Config->DebugDwarf = Args.hasArg(OPT_debug_dwarf);
@@ -1120,6 +1130,23 @@
 
   Config->MapFile = getMapFile(Args);
 
+  if (Config->Incremental && Config->DoGC) {
+    warn("ignoring '/INCREMENTAL' because REF is enabled; use '/OPT:NOREF' to "
+         "disable");
+    Config->Incremental = false;
+  }
+
+  if (Config->Incremental && Config->DoICF) {
+    warn("ignoring '/INCREMENTAL' because ICF is enabled; use '/OPT:NOICF' to "
+         "disable");
+    Config->Incremental = false;
+  }
+
+  if (Config->Incremental && Args.hasArg(OPT_order)) {
+    warn("ignoring '/INCREMENTAL' due to '/ORDER' specification");
+    Config->Incremental = false;
+  }
+
   if (errorCount())
     return;
 
Index: lld/trunk/COFF/Options.td
===================================================================
--- lld/trunk/COFF/Options.td
+++ lld/trunk/COFF/Options.td
@@ -103,6 +103,9 @@
 defm highentropyva : B<"highentropyva",
                        "Enable 64-bit ASLR (default on 64-bit)",
                        "Disable 64-bit ASLR">;
+defm incremental : B<"incremental",
+                     "Keep original import library if contents are unchanged",
+                     "Replace import library file even if contents are unchanged">;
 defm largeaddressaware : B<"largeaddressaware",
                            "Enable large addresses (default on 64-bit)",
                            "Disable large addresses (default on 32-bit)">;
@@ -148,8 +151,6 @@
 
 def functionpadmin : F<"functionpadmin">;
 def ignoreidl : F<"ignoreidl">;
-def incremental : F<"incremental">;
-def no_incremental : F<"incremental:no">;
 def nologo : F<"nologo">;
 def throwingnew : F<"throwingnew">;
 def editandcontinue : F<"editandcontinue">;
Index: lld/trunk/test/COFF/incremental.test
===================================================================
--- lld/trunk/test/COFF/incremental.test
+++ lld/trunk/test/COFF/incremental.test
@@ -0,0 +1,66 @@
+# RUN: yaml2obj < %p/Inputs/export.yaml > %t.obj
+# RUN: lld-link -out:%t.dll -dll %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -incremental %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=WARN-REF %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -incremental %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -debug %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -debug %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=KEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -debug -incremental:no %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -debug -incremental:no %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -opt:icf %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -opt:icf %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -incremental -opt:noref,icf %t.obj 2>&1 \
+# RUN:   | FileCheck -check-prefix=WARN-ICF %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -incremental -opt:noref,icf %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -debug -opt:icf %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -debug -opt:icf %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -opt:ref %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -opt:ref %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -incremental -opt:ref %t.obj 2>&1 \
+# RUN:   | FileCheck -check-prefix=WARN-REF %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -incremental -opt:ref %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# RUN: lld-link -out:%t.dll -dll -debug -opt:ref %t.obj 2>&1 \
+# RUN:   | FileCheck -allow-empty -check-prefix=NOWARN %s
+# RUN: touch -t 198002011200.00 %t.lib
+# RUN: lld-link -out:%t.dll -dll -debug -opt:ref %t.obj
+# RUN: ls -l %t.lib | FileCheck -check-prefix=NOKEEP %s
+
+# NOWARN-NOT: ignoring '/INCREMENTAL'
+# WARN-ICF: ignoring '/INCREMENTAL' because ICF is enabled; use '/OPT:NOICF' to disable
+# WARN-REF: ignoring '/INCREMENTAL' because REF is enabled; use '/OPT:NOREF' to disable
+# KEEP: {{Feb 1 1980|1980-02-01}}
+# NOKEEP-NOT: {{Feb 1 1980|1980-02-01}}
Index: lld/trunk/test/COFF/unchanged-importlib.test
===================================================================
--- lld/trunk/test/COFF/unchanged-importlib.test
+++ lld/trunk/test/COFF/unchanged-importlib.test
@@ -1,7 +0,0 @@
-# RUN: yaml2obj < %p/Inputs/export.yaml > %t.obj
-# RUN: lld-link -out:%t.dll -dll %t.obj
-# RUN: touch -t 198002011200.00 %t.lib
-# RUN: lld-link -out:%t.dll -dll %t.obj
-# RUN: ls -l %t.lib | FileCheck --check-prefix=CHECK %s
-
-# CHECK: {{Feb 1 1980|1980-02-01}}